1. Field of the Invention
The present systems and methods relate to electrical power converter systems, and particularly to electrical power converter systems suitable for photovoltaic and other periodic applications.
2. Description of the Related Art
Electrical power converter systems are used to transform and/or condition electrical power in a variety of applications. For example, electrical power converter systems may transform AC power from a power grid to a form suitable for a standalone application (e.g., powering an electric motor, lights, electric heater, household or commercial equipment, telecommunications equipment, computing equipment, uninterruptible power supply (UPS)). Also for example, electrical power converter systems may transform power from a standalone power source such as an array of photovoltaic cells, fuel cell system, micro-turbine, or flywheel, for use in a standalone application and/or for export to, or by, a power grid.
The electrical power converter system may comprise one or more subsystems such as a DC/AC inverter, DC/DC converter, and/or AC/DC rectifier. Typically, electrical power converter systems will include additional circuitry and/or programs for controlling the various subsystems, and for performing switching, filtering, noise and transient suppression, and device protection.
In many power conversion applications, it is highly desirable to realize the maximum efficiency possible. For example, in photovoltaic applications the cost of photovoltaic arrays is still relatively high, and the physical area occupied by photovoltaic arrays may be undesirably large, particularly where real estate is at a premium. Thus it is desirable to use the least number of photovoltaic cells as possible to achieve the desired power output.
Many power conversion applications are periodic in nature. For example, typical photovoltaic applications are strongly influenced by the relative movement of the sun. The time that the sun rises and/or sets, and the relative position of the sun in the sky throughout the day, determines the amount of power that the photovoltaic cells may generate. Further, the relative position of the sun throughout the year determines the amount of power the photovoltaic cells may generate, and determines the time of sunrise and sunset. Similarly, micro-turbine applications such as hydroelectric power generation may experience a similar periodicity, for example, as water flows increase due to rain or melting snow, on a daily and/or seasonal basis.
It is desirable to have a method and apparatus for converting power that makes the maximum use of the power generated by a power source, such as a photovoltaic array or micro-turbine. However, coupling the electrical power converter system to the power grid before sufficient power is being generated by the power source will result in the electrical power converter system disadvantageously dissipating some power from the power grid, for example, via a transformer in the electrical power converter system. Thus, it is desirable to have a relatively inexpensive, reliable and electrically efficient method and apparatus for electrical power conversion that switches ON or “wakes” the electrical power converter system as early as possible in the power generation cycle, but not before sufficient power is being generated. The present systems and methods are directed at these issues and provide further related advantages.